The rotor blade pitch angles during start up and during operation are essential for any wind turbine's generator power production. For stall-regulated wind turbines the stall level (maximum generator power production) is determined by the air density and the rotor blade pitch angle. For pitch-regulated wind turbines from cut-in wind speed to rated maximum wind turbine generator power production, the blades are supposed to be pitched to extract the maximum power possible. At higher wind speeds and until cut-out wind speed then blades are supposed to be pitched to safely deflect the excess wind power.
It is therefore desirable that the individual blade pitch angles under any rotor position and any wind condition is adjusted correctly to obtain the best possible generator power production and/or to control the turbine max generator power production and loads to be within the specifications. In addition, for both stall regulated wind turbines and pitch regulated wind turbines, if the blade pitch angles of the individual rotor blades at a specific 360° rotor position during start up and operation are not identical, the rotor will not be in balance, resulting in excessive loads on the entire wind turbine and foundation and the generator power production will be influenced in a negative way.
Typically over time the blade pitch system and the blades will experience different kinds of wear and tear and damages during operation as for example stall strips and vortex generators falling off, blade surface cracking and falling off, lightening damages etc. which has a negative impact on the generator power production and loads due to imbalance of the rotor system and reduced aerodynamic efficiency of the individual blades and the entire rotor during operation. This kind of damages is typically inspected only during still stand and by service people using expensive lifts, rope climbing systems or drones.
Over time the blade pitch system will experience mechanical wear and tear and different kinds of damages leading to differences in individual blade pitch angles adjustments etc. during start up and during operation which has a negative impact on the aerodynamic efficiency of the individual blades and the entire rotor and in consequence hereof on generator power production and which will also increase loads.
This kind of mechanical wear and tear related to the blade pitch systems is typically inspected only during still stand and by using traditional camera technology and visual inspection.
Due to production tolerances, from the time of installation there can be different kinds of internal structural differences in the blades and over time there can be changes in the individual blade structure leading to relative blade pitch angle misalignment, difference in blade aerodynamic efficiency, dynamics and imbalance in the rotor system which has a negative impact of the generator power production and increase loads.
This kind of structural changes is typically inspected only during still stand and using different methods.
Any imbalance in the rotor system influence in a negative way the loads on different components in wind turbine, reduce lifetime of those components and lead to consequential damages on for example the foundation etc.
Additionally it is desirable to be able to validate how the blade behaves under different load conditions as variations in the production process might influence the blade's geometry as well as the actual aerodynamic and mechanical function, tolerances and adjustment may influence the individual blade pitch during operation.
Another challenge for condition monitoring of blades, the rotor, generator power production and the tower of a wind turbine is detecting different types of blade damage, any unbalance in individual blade and rotor aerodynamic efficiency, unwanted tower movements and unwanted fluctuations in the generator power production from the wind turbine.
Currently, there is no real-time health overview and condition monitoring of blades and rotors on individual wind turbines and on wind turbine fleets.
Damage can occur right after inspections and this kind of manual inspection is also an expensive process due to WTG down-time during manual inspections, and the process can only be performed under certain weather conditions.
These issues are magnified for offshore locations, where wind farms are considerably larger, salt crystals can be a major cause of erosion and cause moisture diffusion within the blade structure and often the turbines are located far from land and workers must be transported to the off shore site by boat or helicopter every day and the use of lifts and platforms is very difficult due to the swell of the sea.
Consequently, wind farm operators and OEMs have been searching for a condition monitoring system for blades and rotors on individual wind turbines and blades and rotors on wind turbine fleets capable of detecting adverse conditions and predicting failures, in order to help minimize risks and prioritize preventive maintenance and repairs, including strain gauges, acoustics, lasers and thermography—but until now with limited success.
Additional to these facts the basic setting of the traditional condition monitoring wind direction measurement equipment and the wind speed measuring equipment is made during the manufacturing process and typically every second year these instruments are exchanged during service using different positioning and alignment methods, well knowing that these methods are not accurate—due to different accepted tolerances during the manufacturing and servicing process.
Another example is the turbulent fluctuations of wind speed and wind inflow angle impacts on the aerodynamic efficiency of the blades and the entire rotor and influence considerably in a negative way the fatigue life of key components of a wind turbine. Furthermore the generator power production will be influenced in a negative way.
The wind inflow angles can change and the level of turbulence hitting the rotor can be increased or changed under certain conditions, i.e. actual pitch adjustment, operation downstream of another operating wind turbine, downstream of a building or another obstacle, downstream of a patch of trees, downstream of upwind terrain effects as slopes and ridgelines etc.
Today the impact of expected turbulence and relative differences in wind inflow angles will normally be mitigated by having a wind sector management plan which is based on wind measurements on the wind farm sites and “imperfect” computer models and assumptions attempting to predict adverse turbulence loads on the individual wind turbines. Based on these models production output is reduced or wind turbines are shut down at certain wind directions/wind sectors, when the computer calculations conclude such expected conditions where the wind turbulence and wind inflow angle may negatively affect the wind turbine lifetime typical for certain pre-specified combinations of wind direction and wind speed. This measure is called “Wind sector management”.
Reducing energy output or shutting down wind turbines obviously lead to a decrease in energy produced by the wind turbine, and this is therefore highly desirable and there is a need for better technologies for measuring and monitoring turbulence and/or wind inflow angle conditions hitting the rotor of individual wind turbines in each wind sector for defining criteria's for a more optimal wind sector management plan only limiting generator power production or shutting down wind turbines when turbulence levels and/or wind inflow angle are actually above permissible limits.
Another example is if the wind direction measurement is not correct, obviously the wind turbine will operate with yaw misalignment, resulting in excessive loads on key components and the entire turbine and the generator power production will be influenced in a negative way.
Thus there is a need for better technologies for measuring and condition monitoring yaw misalignment, relative blade pitch misalignment, turbulence, wind inflow angle etc. which this invention suggest can be done by combining rotor behaviour measurements and generator torque and generator power production measurements for defining criteria's for more optimal yaw and blade pitch algorithms and adds totally new dimensions to this kind of monitoring.
It is therefore highly desirable to have a condition monitoring system combined with a reliable communication system providing instant alarm from and communication to the wind turbine for the receiver to receive earliest possible any instant alarm signal from the wind turbine and for the receiver to be able to stop the operation of the wind turbine remotely when needed to prevent the wind turbine to operate with misalignments, failures to develop or even to prevent catastrophic failures. Traditional communication methods can be used.
On other words Wind Resource Inflow Characteristics, is important for the basic design of a turbine and specifically for managing the operation of the rotor.
However, the nature of our energy source is very variable—it will come from any of the 360 degrees, the density during the year varies and the force of the wind over time changes intensely—you can even find different wind speeds and directions at different rotor heights.
Initially the control algorithms for modern wind turbines were relying on “primitive” wind vanes and anemometers located in turbulences behind the rotor measuring a minimal fraction of the rotor swept area to control the orientation of the rotor into the wind. Today we know that what is measured at hub height in turbulence behind the rotor can be radically different from the wind the entire rotor is seeing, and the control algorithms of new wind turbines are therefore relying on smarter wind vanes and more reliable anemometers, but these instruments are still measuring the wind in turbulences behind the rotor at hub height and now, considering the development in rotor size, in a much smaller fraction of the rotor swept area.
WO 2015/001301 A1 discloses a system for mapping a wind field upwind from a wind turbine. The mapping of the wind field is combined with other sensor elements for data collection used to improved wind turbine performance monitoring and adjustment of the wind turbine by parameters such as blade pitch, yaw control, load management amongst others. The purpose of the system is to improve the performance and protection of the wind turbine by optimized mapping of the wind field.
The system uses the Doppler-effect for mapping the wind field with the novel feature of utilizing a plurality of Doppler beam sources for optimized wind field mapping. A correction factor may be applied to the measured Doppler velocity in order to correct for any known statistical relationship indicating a difference in wind velocity with velocity of particles entrained in the fluid
Thereby, achieving to correct the measurement toward the true wind velocity despite potentially inaccurate measurements.
WO 2012/103668 A1 discloses a method and a control system for operating a wind turbine generator based on measured wind condition for achieving an optimized operation of the wind turbine. The method measures wind conditions upwind of the wind turbine at two locations at different distances from the wind turbine and measures operation parameters on the wind turbine. Based on the measurements two generator speeds are calculated: the present generator speed based on measurements on operation measurements on the wind turbine, and a forecasted generator speed based on the measured wind conditions. The operation of the wind turbine is optimized by correcting the generator speed from the calculated present generator speed to the forecasted generator speed. Thereby, achieving a method and a control system for operating a wind turbine, which adjusts the operation of the wind turbine, based on the measured wind conditions in two distances prior to the event of these wind conditions actually hitting the wind turbine, or in other words, achieving a feed-back method with sufficient relevant measured wind data, and with sufficient time to adjust the operation of the wind turbine to the measured wind conditions to improve the power output while preventing overspeed of the wind turbine.
This invention suggest that with combining information from new leading-edge technologies we can now sense and monitoring the wind impact, shear and characteristics of the entire rotor swept area, diagnosing for example electric power fluctuation, tower movements, yaw misalignment of the rotor plane, the actual mechanical function, tolerances and adjustment and the behaviour and the aerodynamic efficiency of individual rotor blades at any 360° position and of the entire rotor at any 360° position and measuring and condition monitoring of turbulence and/or wind inflow angle conditions hitting the rotor on the individual wind turbines.
This new information provided by this invention to the wind turbine controller can be used to optimize the aerodynamic efficiency of the individual blades and of the entire rotor and in consequence hereof obtaining the best possible generator power production and lowest loads to be within the specifications and prevent premature wear and tear on turbine components.